This invention relates to measurement devices, and more particularly to a system and method for determining the quality and other parameters of fluids and for dynamically ensuring repeatability of the measurements through in situ cleaning of measurement surfaces.
Transducers for measuring liquid level and other parameters are often used in vehicles, industrial equipment and other systems and components. The electrical output of such transducers change in response to a change in the liquid being measured, and is typically in the form of a change in resistance, capacitance, current flow, magnetic field, frequency, and so on. These types of transducers may include variable capacitors or resistors, optical components, Hall Effect sensors, strain gauges, ultrasonic devices, and so on.
In vehicles, industrial equipment and other systems powered by diesel fuel, a Selective Catalytic Reduction (SCR) system has been used to inject urea—a liquid-reductant agent—through a catalyst into the exhaust stream of a diesel engine. Urea sets off a chemical reaction that converts nitrogen oxides in the exhaust into nitrogen and water, which is then harmlessly expelled through the vehicle tailpipe. Previous urea quality sensor solutions have attempted to address industry quality control by ensuring that a specific quality of urea can be delivered into the exhaust gas stream. If the engine is operated without urea solution in the onboard urea tank, excessive NOx emissions can occur. Using a urea quality sensor, the SCR system can monitor the contents of the urea tank to alert an operator and/or system that the urea tank has been filled with other fluids, e.g., with tap water, coolant, windshield wiper fluid, oil, incorrect concentrations of urea solutions, and so on, instead of the correct concentration of urea solution. The introduction of a urea quality sensor into the SCR system also reduces the risk of tampering or accidental mis-filling and helps ensure compliance to environmental legislation, thus satisfying concerns of users and legislators alike. The urea quality sensor is intended to contribute to the overall success of SCR as a NOx reduction technology.
However, prior art solutions for measuring the presence or absence of the required urea concentration, such as refractive index measurements, capacitive, acoustic, and other known techniques, have been unable to measure the urea concentration with any degree of suitable accuracy to meet rigid industry and legislative requirements.
Moreover, the repeatability of such measurements has been lacking, even in laboratory-grade instrumentation, especially where the fluid quality and/or fluid properties are being measured under static conditions where it may be impractical to clean the measuring surfaces after each measurement, and more especially under continuous flow conditions where the system cannot be opened for cleaning, such as in above-mentioned SCR systems. Components of the fluid itself, undesirable contaminants present in the fluid through error or improper handling or filtering, as well as contaminants leaching into the fluid from surrounding surfaces in contact with the fluid can build up on measuring surfaces and cause a change in the measurement of the fluid, and thus lead to inaccurate results.
Besides contamination of the measuring surfaces associated with SCR systems, other fluids that may be measured, including but not limited to gasoline, oil, diesel fuel, coolant, and so on, associated with a vehicle, as well as other fluids in various industries, may also create undesirable deposits on the measuring surfaces, thus creating measurement errors.
It would therefore be desirous to provide a system and method for determining at least one fluid property including fluid quality, composition, and other parameters with a higher degree of accuracy than prior art systems in order to quantify whether or not proper fluid and/or the proper concentrations of fluids are being used in vehicles, machinery, and so on, while dynamically reducing or eliminating the collection of contaminants at least on measuring surfaces of the system.